Sheet gripper apparatus for a cutting and creasing press

ABSTRACT

A pair of endless chains are reeved about spaced pairs of sprockets and transverse gripper bars are connected to the endless chain in spaced relation to each other. The sprockets are driven to propel the chains with transverse gripper bars secured therethrough through the cutter and creaser section, stripping section and delivery section of the press unit. The gripper bars have a plurality of gripper members secured thereto and extending rearwardly therefrom. The gripper members include a rigid base or pad member extending rearwardly from the gripper bar and a resilient sheet engaging gripper finger positioned in overlying relation with the fixed rearwardly extending rigid pad member. The gripper finger actuator includes vertical pin members extending upwardly through vertical portions in the transverse gripper bar with the upper edge portions abutting the underside of the resilient gripper fingers. The lower edge portions of the pin members have rollers thereon arranged parallel to the longitudinal axis of the transverse gripper bars. An elongated plate is slidably secured to the underside of the transverse gripper bars and has portions abutting the respective rollers connected to the vertical pins. The plate members have an inclined portion adjacent to the respective rollers so that axial movement of the plate member relative to the gripper bar moves the roller members along the inclined portions of the plate to move the resilient gripper finger end portions away from the fixed pad of the gripper member. The plate unit includes cam followers connected at one end to the transverse gripper bar and at the other end to the slidable plate. The cam followers are arranged to move the slidable plate longitudinally relative to the gripper bar to open the gripper members at preselected locations along the press unit.

inns Patent 1 11 3,809,390 51 May 7,1974

[ SHEET GRIPPER APPARATUS FOR A CUTTING AND CREASING PRESS [75]Inventor: Franz N Lenoir,'Marcinelle,

Belgium [73] Assignee: Miller Printing Machinery C0.,

' Pittsburgh, Pa.

22 Filed: Jan. 12, 1972 21 Appl. No.: 217,303

[52] US. Cl. 271/204, 198/180 Primary Examiner-Evon C. Blunk AssistantExaminer-Bruce H. Stoner, Jr. Attorney, Agent, or FirmStan'ley J. Price,Jr.

57 ABSTRACT A pair of endless chains are reeved about spaced pairs ofsprockets and transverse gripper bars are connected to the endless chainin spaced relation to each other.

ca c2 Canada 271/79 The sprockets are driven to propel the chains withtransverse gripper bars secured therethrough through the cutter andcreaser section, stripping section and delivery section of the pressunit. The gripper bars have a plurality of gripper members securedthereto and extending rearwardly therefrom. The gripper members includea rigid base or .pad member extending rearwardly from the gripper barand a resilient sheet engaging gripper finger positioned in overlyingrelation with the fixed rearwardly extending rigid pad member. Thegripper finger actuator includes vertical pin members extending upwardlythrough vertical portions in the transverse gripper bar with the upperedge portions abutting the underside of the resilient gripper fingers.The lower edge portions of the pin members have rollers thereon arrangedparallel to the longitudinal axis of the transverse gripper bars. Anelongated plate is slidably secured to the underside of the transversegripper bars and has portions abutting the respective rollers connectedto the vertical pins. The plate members have an inclined portionadjacent to the respective rollers so that axial movement of the platemember relative to the gripper bar moves the roller members along theinclined portions of the plate to move the resilient gripper finger endportions away from the fixed pad of the gripper member. The plate unitincludes cam followers connected at one end to the transverse gripperbar-and at the other end to the slidable plate. The cam followers arearranged to move the slidable plate longitudinally relative to thegripper bar to open the gripper members at preselected locations alongthe press unit.

3 Claims, 9 Drawing Figures PATEYEWY SHEU 1 [I 3 PMWEUMAY 7 m4 III SHEET2 BF 3 SHEET GRIPPER APPARATUS FOR A CUTTING AND CREASING PRESSCROSS-REFERENCE TO RELATED APPLICATIONS A cutter and creaser unitsimilar to that described herein is claimed in co-pending United Statesapplication 83,335, filed on Oct. 23, 1970 now US. Pat. No. 3,653,304,by the same inventor and assigned to the same assignee and is entitledApparatus for Cutting and Creasing Sheets.

BACKGROUND OF THE INVENTION 1. Field of the Invention.

This invention relates to sheet gripper apparatus and more particularlyto sheet gripper apparatus for a cutting and creasing machine.

2. Description of the Prior Art v Sheet grippers that include transversegripper bars with a plurality of gripper assemblies thereon are knownand disclosed in US. Pat. Nos. 2,703,364; 2,775,197; 3,042,398 and3,502,324. The conventional sheet grippers have transverse gripper barswith rotatable gripper actuating shafts connected to the gripper,fingers. The gripper actuator shafts 1 are rotated by means of camsconnected to the pressside frames. The gripper finger actuator bars arerotated by suitable cam followers associated therewith to open and closethe grippers. The known arrangement of separate rotatable gripper fingeractuator bars requires substantial space within the press to positionthe gripper apparatus and further requires substantial space for thegripper finger shaft actuator cams. The torsionimparted tothe gripperfinger actuator shaft requires the shaft to have a substantialmass toprevent torsional deflection and uneven opening of the gripper fingers.

There is a need for a sheet gripper apparatus of the transverse gripperbar type that requires a minimum amount of space for both the transversegripper bars with the gripper assemblies thereon and for the gripperfinger actuator devices. There is also a need for gripper apparatus thatdoes not subject elements of the gripper assembly to torsional twistingforces during the opening and closing of the gripper assemblies.

SUMMARY OF THE INVENTION This invention relates to a sheet grippermechanism that includes a transverse gripper bar having a body portionwith a plurality of vertical passageways therein. The gripper bar bodyportion has a top surface and a bottom surface. The vertical passagewayshave openings in the top surface and bottom surface. Sheet gripperassemblies aresecured to the gripper bar body portion and have a gripperpad portion on the gripper bar body portion top surface adjacent to thevertical passageway. The gripper assemblies have gripper fingers securedto the gripper bar body portion top surface and are positioned inoverlying relation with the vertical passageways. The gripper fingershave sheet engaging portions in overlying relation with the gripperpads. The gripper assemblies are arranged to engage a sheet between thegripper fingers and the gripper pad. Pin members are positioned in thevertical passageways and have a top portion abutting the underside ofthe gripper fingers. Gripper opening apparatus is arranged to move thepin members upwardly in the passageways to move the gripper sheetengaging portions'away from the gripper pads. v

The gripper opening means includes a plate member slidably secured tothe bottom surface of the gripper bar body portion with recessedportions beneath the pin members and cam surfaces adjacent to the pinmembers. A cam member secured to the press frame engages a camfollowersecured to the plate member to periodically move the platemember longitudinally and move the cam portions of the plate member intounderlying relation with the pin members. The plate member has resilientmeans urging the recessed portions of the plate into underlying relationwith the pin members to permit the gripper assemblies to remain in aclosed position until actuated by the cam member secured to the pressframe. A second cam member is secured to the opposite side of the pressframe and is arranged to engage a cam follower connected to the gripperbar body portion while the plate member cam follower is engaged by theother cam member to thereby prevent longitudinal movement of the gripperbar during the opening of the gripper assemblies.

Accordingly, the principal object of this invention is to provide asheet gripper mechanism in which torsional forces are not required toopen or close the gripper assemblies mounted on a gripper bar.

Another object of this invention is to provide a sheet gripper mechanismthat requires a minimum of space in the press and provides uniformdisplacement for the gripper assembly actuator.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in side elevation andpartially in section of a cutter and creaser machine in which sheets ofpaper, cardboard and the like are-conveyed through the machine by asheet conveying apparatus that includes transverse gripper bars with aplurality of grippers positioned thereon.

FIG. 2 is a diagrammatic view in section taken along the line IIII ofFIG. 1, illustrating schematically the various sections of the machineand a transverse gripper bar connected to endless conveyor chains. Cammembers for opening andclosing the gripper members on the transversegripper bar are also illustrated.

FIG. 3 is a fragmentary top plan view of the transverse gripper bar withthe gripper membersextending rearwardly therefrom.

FIG. 4 is a view of a transverse gripper in side elevation and partiallyin section, illustrating the actuating apparatus for opening and closingthe grippers.

FIG. 5 is a bottom plan view of the transverse gripper bar, illustratedin FIGS. 3 and 4.

FIG. 6 is a view in section taken along the line VI-VI in FIG. 3.

FIG. 7 is a view in section taken along the line VII- VII in FIG. 3,illustrating in detail the gripper member and the apparatus for openingand closing the gripper member.

FIG. 7A is a view in section similar to FIG. 7, illustrating the gripperin an open position.

FIG. 8 is a fragmentary plan .view of a portion of the machine,illustrating the cam members secured to the machine side frames.

DESCRIPTION OF THE PREFERRED EMBODIMENTS and 2 there is illustrated acutter and creaser machine generally designated by the numeral that hasasheet feeder unit generally designated by the numeral 12 connected to apress unit generally designated by the. numeral 14. Sheets are fed fromthe feeder unit 12 down a feedboard 16 into the press unit 14 in aconventional manner. The press 14 may, for convenience, be segmentedinto a transfer section 18, a cutter and creaser section 20, a strippersection 22 and a stack or deliverysection 24. The sheets supplied to thepress 14 along the feedboard 16 are moved into side and front registeron the feedboard 16 and are engaged by a gripper mechanism in thetransfer section 18. The sheets are accelerated to press speed byapparatus in the transfer section 18 and fed at press speed to the pressunit 14. i

The press unit 14 has sheet conveyor apparatus generally designated bythe numeral 25 that includes a pair of endless chains 26 and 28 mountedon pairs of idler sprockets 30 and 32 adjacent the transfer section 18and a pair of drive sprockets 3.4 and 36 adjacent the delivery section24. The endless conveyor chains 26 and v 28 have a plurality oftransverse conveyor bars generally designated by the numeral 38connected thereto in preselected spaced relation to each other. Theconveyor bars 38 have a plurality of grippers generally des ignated bythe numeral 40 thereon that are arranged to open and engage the edge ofthe sheet in the transfer section 18 of the press and convey the sheetthrough the cutter and creaser section 20 and stripper section 22 to thedelivery section 24 where the grippers 40.are arranged to open andrelease the sheet.

Positioned within the cutter and creaser section 20 are a pair ofplatens 42 and 44 that are arranged to periodically move into abuttingrelation with each other while asheet engaged by grippers 40 ontransverse bar 38 is positioned therebetween to cut and crease thesheet. The transverse bar 38 to which the sheet is engaged has advancedbeyond the front edge of the platens 42 and 44 when the platens moveintocutting relation with the sheet. It should be noted that the platens42 and 44 and the sheets therebetween are moved toward the strippersection 22 while the sheet is being cut and creased. A drive motor 46 isconnected by shafting and gears to drive shafts for the platens 42 and44, as is more completely described in copending U.S. application Ser.No. 83,335 now U.S. Pat. No. 3,653,304 and does not form a part of thepresent invention other than to provide a drive for the drive sprockets34 and 36 for the sheet conveyor apparatus 25.

Within the stripper section'22 there are other platens 48 and 50 thatare arranged to periodically move into abutting relation with each otherand strip or remove the cut out portions from the sheet as the sheet isconveyed through the stripper section 22 to the delivery section 24 bythe sheet conveyor apparatus 25. A drive shaft 52 drives the eccentricshaft of the stripper platens to move the platens 48 and 50 in timedrelation with the cutter platens 42 and 44. It is essential that thesheet conveyor apparatus 25 deliver the sheets to the cutter and creasersection 20 and to the stripper section 22 in proper register with therespective platens so that the respective cuts and creases are impressedon the sheet at the desired locations and the cut out portions removedfrom the sheet. The stripper platens 48 and 50 are driven in timedrelation to the cutter'and creaser platens 42 and 44 by gearing and theshaft 52. A shaft 54 is connected to the drive gearing for the stripperplatens and by means of a bevel gear 56 is arranged to drive adifferential drive mechanism (not shown) for the shaft 58 on which thedrive sprockets 34 and 36 are mounted. The drive mechanism for the shaft58 is a differential drive mechanism that is arranged to rotate theshaft 58 at difierent angular velocities so that the sheet engaged bythe conveyor apparatus 25 moves in timed relation to the respectiveplatens in the cutter and creaser section 20 and stripper section 22.

The gripper members 40 on the transverse. gripper bars 38 are arranged,and later described, to release the sheet inthe delivery section 24 sothat the sheets are deposited on a stack generally designated by thenumeral 60 in the delivery section 24.

Now referring to FIGS. 3-8, the sheet conveyor apparatus generallydesignated by the numeral 25 is illustrated in detail and includes aplurality of transverse bars 38 arranged in predetermined spacedrelation to each'other. The transverse bars 38 have an elongatedgenerally rectangular body portion 62 with a plurality of vertical bores64 therein. Suitable cylindrical bushings 66 are positioned in thevertical bores 64.

Rearwardly extending gripper pad members 68 are secured to the uppersurface of the bar body portion 62 and have a serrated surface 70. Aflexible resilient gripper finger 72 is secured to the upper surface ofthe bar body portion 62 at one end adjacent the front by bolt members74. The rear end of the gripper finger 72 has an arcuate depending edgeportion 76 which is arranged to abut the serrated surface of gripper pad68. As is illustrated in FIG. 7A, the front edge 78 of sheet S ispositioned in overlying relation with the serrated portion 70 of gripperpad 68 and the arcuate portion 76 of finger 72 is arranged to move intoabutting relation with the upper surface of the sheet front edge 78 andthus engage the front edge of sheet S to the transverse gripper bar 38for movement therewith.

The bores 64 in the gripper bar body portion 62 are aligned with thegripper finger 72 so that the gripper finger 72 is. in overlyingrelation with the bores 64in the gripper bar body portion 62.

Positioned in each of the bores 64 are vertically extending pin members80 that have a rounded top'edge 82in abutting relation with theunderside of the gripper finger 72 and a roller member 84 rotatablymounted adjacent the other end and extending downwardly therefrom. Therollers 84 are mounted with their a-xis transverse to the longitudinalaxis of the gripper bar 38. An elongated plate member 86 is slidablypositioned in abutting relation with the underside of the gripper barbody portion 62 and is maintained in this position by bridge-like strapmembers 88 secured to the underside of the transverse bar body portion62. The elongated plate 86 has recessed portions 90, as best illustratedin FIG. 5, beneath each of the rollers 84. The recessed portions 90 havean inclined cam surface 92 on which a Q the roller 84 is arranged tomove as the plate 86 is moved longitudinally relative to the transversebar body portion 62.

The transverse bar 38 has an arm member 94 secured to the plate edgeportion 96 which is adjacent to the chain 28. The arm member 94 issuitably secured to the plate 86 by screw 98 and has a cam roller orfollower 100 rotatably secured thereto and depending therefrom. The camroller 100 is arranged to move in the track 102 of cam member 104 thatis secured to the press frame 106. The cam member 104 is clearlyillustrated in FIG. 6 with the cam track 102. As is illustrated in FIG.2, a pair of cam members 104 is suitably secured to the press frame 106adjacent the transfer section 18 and adjacent the delivery section 24and is arranged to open the gripper fingers 72 at these locations.

As the sheet conveyor apparatus 25 moves the transverse bar 38,illustrated in phantom in FIG. 8, in the direction indicated by thearrow, the cam roller 100'enters the throat 108 of cam track 102 andfollows the arcuate track 102 to move the cam follower 100 laterallytoward the chain 28. Movement of the cam-follower 100 toward the chain28 moves the slidable plate 86 connected thereto longitudinally relativeto the transverse bar body portion 62 to move the recessed portions 9.0of the plate 86 so that the inclined portions 92 are moved beneath therollers 84 to displace the pins 80 upwardly and move the gripper finger72 to the open position as illustrated in FIG. 7A.

Connected to the opposite end 110 of slidable plate 86 is a springmember 112. The spring member 112 is connected at the other end to anarm member 114 that is rigidly secured to the transverse bar bodyportion 62 by screw member 116. A stop member 118 abuts the end 110 ofslidable plate 86 to limit movement of the plate 86 toward the chain 26.With this arrangement the cam 104 through cam follower 100 moves theslidable plate 86 laterally to open the gripper fingers and the spring112 moves the slidable plate 86 in the opposite direction against thestop 118 to position the rollers 84 of pins 80 in the recessed portions90 of slidableplate 86 so that the resilient fingers 72 of grippers 40are urged into a closed position.

The lateral force exerted by the cam follower 100 in the track 102 ofcam 104 in pulling the plate 86 against the tension of spring 112 pullsthe transverse gripper bar 38 laterally toward the chain 28, as viewedin FIGS. 3 and 4. The chain links have a relatively loose fit and wouldpermit lateral movement of the transverse bar 38 and interfere with theopening and closing of the grippers 40. Also, the opening and closing ofthe grippers would not be uniform. To eliminate the lateral movement ofthe transverse gripper bar 38 the arm member 114 is rigidly secured tothe gripper bar body portion 62 by means of screw 1 16. Cam followerrollers 120 are rotatably secured to the end of the arm member 114 andare arranged to be positioned in the cam track 122 of cam member 124that is rigidly secured to the press frame 126. The cam member 124 ispositioned opposite to the gripper opening cam 104. With'thisarrangement the cam followers 120 move into the straight cam track 122of cam member 124 and provide a rigid nonyieldable support for thetransverse bar 38 as the cam follower 100 moves the plate 86 laterallyto open, the respective grippers. Although apair of cam followers 120are illustrated in the drawings, it should be understood a single camfollower may also be employed.

It is desirable to permit the transverse gripper bar 38 to move relativeto its connection to the respective chains 26 and 28 and therebyaccurately register the transverse bar 38 and the sheet conveyedtherewith in the cutting and creasing section 20 and the strippingsection 22 of the press unit 14. The transverse gripper bar body porion62 has similar end members 130 and 132 (FIGS. 3 and 5) secured theretoby bolts 134. The

end members have a recessed intermediate portion 136 with outwardlyextending spaced flanges 138 and 140.

Chain connector members 142 and 144 are similar in construction and havea body portion 146 with spaced pin members 148 and 150 extendinglaterally therefrom. The pin members extend through receiving bores 152and 154' in the links of chains 26 and 28 to thus connect the chainconnecting members 142 and 144 to two adjacent links of the respectiveendless chains 26 and 28. The chain connector members 142 and 144 haveinwardly extending arms 156 and 158 that are positioned within recessedportion 136 of end members and 132 between the respective flanges 138and 140. The flanges 138 and have a pair of pin members 160 and 162suitably secured therein in parallel spaced relation to each other andextend across the recessed portion 136. The arms 156 and 158 of chainconnector members 142 and 144 have bores therethrough and are slidablypositioned on the pins 160 and 162. Spring members 164 and 166 extendaround the pins 160 and 162 and at one end abut the arm 156 of chainconnector members 142 and 144 and at the other end abut stops 168 and170 on pins 160 and 162. With this arrangement the transverse bar bodyportion 62 is movable longitudinally relative to the chain connectors142 and 144.- v

Suitable levers or stops (not shown) may be provided in the cutter andcreaser machine where register of the sheets conveyed therethrough isessential as, for example',-in the cutter and creaser section 20 andstripper section 22 when the respective platens move into operativerelation with the sheet. The levers or stops are arranged to abut theedges 172 of end members 130 and 132 and push members 130 and 132 withthe transverse bar 38 connected thereto in the direction of movement ofthe transverse cutter bar a predetermined amount to provide register ofthe sheet. The springs 166 and 168 are compressed and the end members130 and 132 ,connected at each end of the transverse bar 38 premitmovement of the bar 38 toward relative to the chains and the chainconnector members 142 and 144. When registration is no longer required,the levers or stop members release the force exerted on the edges 172and springs 166 and 168 move the bar to the position illustrated in FIG.3.

It will be apparent with the previously described gripper bar that theaxis of the gripper bar 38 is substantially in the same plane as thechains 26 and 28, as is clearly illustrated in FIG. 4. Such aconfiguration reduces the space required for the transverse gripper barsand permits gripper bars of greater thickness and rigidity to be used.

The apparatus for opening and closing the gripper fingers because of thelinear movement does not apply torsional forces to the gripper bar andthere is a uniform displacement or movement of the gripper actuator toprovide instantaneous and simultaneous opening of all of the grippers40. Further, with this arrangement, the opening cams, i.e., cams 104,and the rigidi: fying cams, i.e., cams 124, may be positioned atpreselected locations within the press unit 14 without requiringsubstantial space to actuate the grippers. The sheets with the gripperbars are moved into accurate register during the cutting and creasingand stripping operations by the resilient connection between thetransverse 7 gripper bar body portion 62 and the chain connector members142 and 144.

According to the provisions of the patent statutes, I V have explainedthe principle, preferred construction, and mode of operation of myinvention and have illustrated and described what I now consider torepresent its best embodiments. However, I desire to have it understoodthat, within the scope of the appended claims, the invention may bepracticed otherwise than as specifically illustrated and described.

I claim:

1. A sheet gripper mechanism comprising,

endless chains positioned in spaced parallel relation to each other, atransverse gripper bar having a body portion with a plurality ofvertical passageways therein,

said gripper ,bar body portion having atop surface and a bottom surface,said ,vertical passageways have openings in said top surface and saidbottom surface,

said gripper bar positioned transversely between said endless chains,

means connecting the end portions of said gripper bar to said endlesschains,

gripper assemblies having gripper'pads on said gripper bar body portiontop surface adjacent to said vertical passageways, said gripperassemblies having gripper fingers secured to said gripper bar bodyportion top surface and positioned in overlying relation with saidverti- 30 cal passageways, said gripper fingers having sheet engagingportions in overlying relation with said gripper pads, said gripperassemblies arranged to engage a sheet between said gripper fingers andsaid gripper pad,

pin members positioned in said vertical passageways having a top portionabutting the underside of said gripper fingers,

an elongated plate member positioned adjacent to said gripper bar bodyportion bottom surface in underlying relation with said pin members,said plate member being movable relative to said gripper bar bottomsurface,

said plate member having upwardly facing cam surfaces adjacent to thebottom portion of said pin members,

said plate member having an end portion with a cam follower thereon,fixed members positioned adjacent to said chains a first fixed cammember secured to one of said fixed members, said first fixed cam memberarranged to engage said cam follower secured to the end of said platemember and move said plate member longitudinally relative to saidgripper bar body portion and move said'pin members upwardly in saidpassageways and thereby move said gripper finger sheet engaging portionaway from said gripper pads,

a second cam follower secured to an end portion of said gripper bar bodyportion, and

a second cam member secured to at least one of said fixed members andarranged to engage said second cam follower secured to said gripper barbody portion and prevent longitudinal movement of said gripper bar bodyportion while said cam follower secured to said plate member engagessaid first cam member.

2. A sheet gripper mechanism as set forth in claim 1 which includes,

resilient means secured to said gripper bar body portion and an endportion of said elongated plate member,

stop means on said gripper bar body portion bottom surface arranged tolimit longitudinal movement of said plate member,

said resilient means arranged to urge said plate member against saidstop member to position said plate member recessed portion beneath saidpin member 1 bottom portions.

3. A sheet gripper mechanism as set forth in claim 1 in which said meansconnecting the end portions of said gripper. bar to said chainsincludes,

means to permit limited movement of said. gripper bar body portionrelative to said endless chains.

1. A sheet gripper mechanism comprising, endless chains positioned inspaced parallel relation to each other, a transverse gripper bar havinga body portion with a plurality of vertical passageways therein, saidgripper bar body portion having a top surface and a bottom surface, saidvertical passageways have openings in said top surface and said bottomsurface, said gripper bar positioned transversely between said endlesschains, means connecting the end portions of said gripper bar to saidendless chains, gripper assemblies having gripper pads on said gripperbar body portion top surface adjacent to said vertical passageways, saidgripper assemblies having gripper fingers secured to said gripper barbody portion top surface aNd positioned in overlying relation with saidvertical passageways, said gripper fingers having sheet engagingportions in overlying relation with said gripper pads, said gripperassemblies arranged to engage a sheet between said gripper fingers andsaid gripper pad, pin members positioned in said vertical passagewayshaving a top portion abutting the underside of said gripper fingers, anelongated plate member positioned adjacent to said gripper bar bodyportion bottom surface in underlying relation with said pin members,said plate member being movable relative to said gripper bar bottomsurface, said plate member having upwardly facing cam surfaces adjacentto the bottom portion of said pin members, said plate member having anend portion with a cam follower thereon, fixed members positionedadjacent to said chains a first fixed cam member secured to one of saidfixed members, said first fixed cam member arranged to engage said camfollower secured to the end of said plate member and move said platemember longitudinally relative to said gripper bar body portion and movesaid pin members upwardly in said passageways and thereby move saidgripper finger sheet engaging portion away from said gripper pads, asecond cam follower secured to an end portion of said gripper bar bodyportion, and a second cam member secured to at least one of said fixedmembers and arranged to engage said second cam follower secured to saidgripper bar body portion and prevent longitudinal movement of saidgripper bar body portion while said cam follower secured to said platemember engages said first cam member.
 2. A sheet gripper mechanism asset forth in claim 1 which includes, resilient means secured to saidgripper bar body portion and an end portion of said elongated platemember, stop means on said gripper bar body portion bottom surfacearranged to limit longitudinal movement of said plate member, saidresilient means arranged to urge said plate member against said stopmember to position said plate member recessed portion beneath said pinmember bottom portions.
 3. A sheet gripper mechanism as set forth inclaim 1 in which said means connecting the end portions of said gripperbar to said chains includes, means to permit limited movement of saidgripper bar body portion relative to said endless chains.